Exhaled human breath typically comprises approximately 78% nitrogen, 15-18% oxygen, and 4-6% carbon dioxide. The remaining small fraction of exhaled breath generally consists of saturated water vapor and trace levels of more than 1000 volatile organic compounds (VOCs) with concentrations ranging from parts per trillion (pptv) to parts per million (ppmv).
The specific composition of a person's breath can indicate various health conditions. For example, acetone is a VOC in exhaled human breath that can indicate diabetes, heart disease, epilepsy, and other conditions. A person who is in a state of ketosis will have an increased breath concentration of acetone resulting from the body's production of ketone bodies. Acetone is also produced by ketosis resulting from a restricted calorie weight loss and/or exercise program. This acetone production is the result of metabolism of fat. Hence, a breath acetone content measurement can be used as an indication of a medical condition or of fat burning during a diet and/or program to show the effectiveness of the program.
Sensors such as those for detecting acetone in breath samples can be particularly sensitive to the manner in which the sensor is exposed to the sample being tested. While repeatable and accurate results can be obtained in a lab setting by exposing the sensors to a sample in a controlled manner, it is often desirable to analyze a breath sample outside of a lab setting.
Consumer devices and/or portable devices for testing breath samples are typically used outside of a controlled laboratory setting. Such devices generally take a live breath sample and expose the sensor directly to the exhaled human breath, resulting in readings that are neither repeatable nor accurate. Collecting live breath samples, particularly from multiple subjects, causes factors to vary that can otherwise be held relatively constant in the lab gas setup described above. These factors include velocity of exhaled breath, dynamic vapor pressure, duration of exhalation, total volume and individual size of exhaled droplets, and variable oxygen and acetone concentrations that are dependent on which part of the exhaled breath is sampled from (i.e. mouth air, deep lung air, or somewhere in between). Collectively and individually, these variables contribute to poor repeatability and inaccurate measurements.
Known sensors also suffer from designs that inhibit accuracy and repeatability, even when exposed to a controlled, consistent flow of a breath sample. One example of a known acetone sensor 600, shown in FIG. 18, includes tungsten trioxide (WO3) disposed on an alumina or anodic aluminum oxide (AAO) substrate. This and similar sensors have typically been packaged in cylindrical leaded components, such as a standard TO-5 header 602, like the one shown in FIG. 16. While TO-5 and similar headers are readily available, they are expensive, even at high manufacturing volumes. In addition, gas sensors housed in a TO type header are typically exposed to an air sample via diffusion, either through a mesh screen 604 or a hole in the case. As a result, such sensors are typically not well-suited for applications involving a sample having a controlled mass flow.
Acetone sensors are useful for detecting various health conditions and/or for monitoring the efficacy of diet and exercise programs. The acetone level for diet and exercise is lower than that caused by diabetes. Accordingly, a more sensitive, accurate, and repeatable sensor is required in order to monitor increased acetone levels caused by diet and exercise.
The present disclosure is directed to a breath capture and sampling system that captures a breath sample and provides it to a sensor in a manner that produces accurate and repeatable detection of various breath components. Although the described embodiment is directed toward the detection of acetone in a breath sample, it will be appreciated that alternate embodiments are possible wherein other sample components are sensed, and such embodiments should be considered within the scope of the present disclosure.